Low-noise image sensor having stacked semiconductor substrates

ABSTRACT

Various embodiments of the present disclosure are directed towards an image sensor. The image sensor includes a first semiconductor substrate having a photodetector and a floating diffusion node. A transfer gate is disposed over the first semiconductor substrate, where the transfer gate is at least partially disposed between opposite sides of the photodetector. A second semiconductor substrate is vertically spaced from the first semiconductor substrate, where the second semiconductor substrate comprises a first surface and a second surface opposite the first surface. A readout transistor is disposed on the second semiconductor substrate, where the second surface is disposed between the transfer gate and a gate of the readout transistor. A first conductive contact is electrically coupled to the transfer gate and extending vertically from the transfer gate through both the first surface and the second surface.

REFERENCE TO RELATED APPLICATION

This Application claims the benefit of U.S. Provisional Application No. 62/806,455, filed on Feb. 15, 2019, the contents of which are incorporated herein by reference in their entirety.

BACKGROUND

Many modern day electronic devices (e.g., digital cameras, optical imaging devices, etc.) comprise image sensors. Image sensors convert optical images to digital data that may be represented as digital images. An image sensor includes an array of pixel sensors, which are unit devices for the conversion of an optical image into digital data. Some types of pixel sensors include charge-coupled device (CCD) image sensors and complementary metal-oxide-semiconductor (CMOS) image sensors. Compared to CCD pixel sensors, CMOS pixel sensors are favored due to low power consumption, small size, fast data processing, a direct output of data, and low manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of a low-noise image sensor having stacked semiconductor substrates.

FIG. 2 illustrates a layout view of some other embodiments of the low-noise image sensor of FIG. 1.

FIG. 3 illustrates a layout view of some other embodiments of the first array of FIG. 2.

FIG. 4 illustrates a layout view of some other embodiments of the first array of FIG. 3.

FIG. 5 illustrates a layout view of some other embodiments of the first array of FIG. 3.

FIG. 6 illustrates a layout view of some other embodiments of the second array of FIG. 2.

FIG. 7 illustrates a layout view of some other embodiments of the second array of FIG. 6.

FIG. 8 illustrates a cross-sectional view of some embodiments of the low-noise image sensor of FIG. 2 taken along line A-A′.

FIG. 9 illustrates a cross-sectional view of some other embodiments of the low-noise image sensor of FIG. 1.

FIG. 10 illustrates a cross-sectional view of some other embodiments of the low-noise image sensor of FIG. 9.

FIG. 11 illustrates a cross-sectional view of some other embodiments of the low-noise image sensor of FIG. 9.

FIG. 12 illustrates a cross-sectional view of some other embodiments of the low-noise image sensor of FIG. 9.

FIG. 13 illustrates a cross-sectional view of some other embodiments of the low-noise image sensor of FIG. 9.

FIGS. 14-28 illustrate a series of cross-sectional views of some embodiments for forming the low-noise image sensor of FIG. 9.

FIG. 29 illustrates a flowchart of some embodiments of a method for forming a low-noise image sensor having stacked semiconductor substrates.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Some complementary metal-oxide semiconductor image sensors (CISs) have an array of pixel sensors. A pixel sensor of the array of pixel sensors comprises an array of photodetectors (e.g., a 2×2 photodetector array) disposed in a semiconductor substrate. In some embodiments, the photodetectors may be separated from one another by an isolation structure (e.g., a full-depth isolation structure). Further, the pixel sensor comprises a plurality of pixel devices (e.g., a transfer gate, a reset transistor, a source follower transistor, and/or a row-select transistor) that are disposed on an active region of the semiconductor substrate. An interconnect structure overlies the semiconductor substrate and the pixel devices, and electrically couples the photodetectors and the pixel devices together, such that the pixel sensor may function properly. The pixel sensor records incident radiation (e.g., photons) using the photodetectors and facilitates digital readout of the recording with the pixel devices.

One challenge with the above CISs is poor noise performance (e.g., random noise, fixed-pattern noise, flicker noise, shot noise, thermal noise, white noise, etc.). One contributor to noise performance is sizes of the plurality of pixel devices (e.g., a size of the source follower device). While the isolation structure may improve full well capacity of the image sensor, the isolation structure may reduce a size of the active region of the semiconductor substrate. Because the isolation structure reduces the size of the active region, the sizes of the pixel devices are typically reduced in order for the pixel devices, the isolation structure, and the photodetectors to be disposed on/in the semiconductor substrate. However, reducing the sizes of the pixel devices negatively affects noise (e.g., due to a size of the source follower device being reduced), thereby contributing to poor noise performance.

Another contributor to noise is a total conductive area of the interconnect structure (e.g., due to an increase in parasitic capacitance). For example, the total conductive area of metal lines, metal vias, and metal contacts disposed over the semiconductor substrate to electrically couple the pixel devices and the photodetectors together. Typically, the location of the pixel devices are at least partially dependent upon the layout of the isolation structure and/or the photodetectors, thereby causing some pixel devices to be disposed a relatively large distance from other pixel devices and/or some of the photodetectors. Thus, some metal lines may extend a relatively large distance in order to electrically couple the some of the pixel devices to the other pixel devices and/or the some of the photodetectors. Accordingly, the total conductive area of the interconnect structure is increased, thereby contributing to poor noise performance.

Various embodiments of the present application are directed toward a low-noise image sensor. The low-noise image sensor includes a photodetector and floating diffusion node disposed in a first semiconductor substrate. A transfer gate is disposed on the first semiconductor substrate. In some embodiments, an isolation structure is disposed in the first semiconductor substrate. A second semiconductor substrate is spaced from the first semiconductor substrate. A readout transistor (e.g., a source follower transistor) is disposed on the second semiconductor substrate, wherein a surface of the second semiconductor substrate is disposed between the transfer gate and a gate of the readout transistor. A conductive contact is electrically coupled to the transfer gate and extends vertically from the transfer gate to the second semiconductor substrate.

Because the second semiconductor substrate is vertically spaced from the first semiconductor substrate, and because the isolation structure is disposed in the first semiconductor substrate and the readout transistor is disposed on the second semiconductor substrate, the isolation structure may not constrain a size of the readout transistor. Thus, the size of the readout transistor may be larger than if the readout transistor and the isolation structure were disposed on a same semiconductor substrate. Accordingly, the low-noise image sensor may have improved noise performance (e.g., due to an increased size of the source follower transistor).

In addition, because the photodetector, the transfer gate, and the floating diffusion node are disposed in/over a different semiconductor substrate than the readout transistor, the readout transistor may be disposed closer to the floating diffusion node than if the readout transistor and the floating diffusion node were disposed on a same semiconductor substrate. Thus, a total conductive area of an interconnect structure may be less than if both the readout transistor and the floating diffusion node were disposed on the same semiconductor substrate. Accordingly, the low-noise image sensor may have improved noise performance (e.g., due to a reduction in total conductive area of an interconnect structure).

FIG. 1 illustrates a cross-sectional view of some embodiments of a low-noise image sensor 100 having stacked semiconductor substrates.

As shown in FIG. 1, the low-noise image sensor 100 comprises a first semiconductor substrate 102. The first semiconductor substrate 102 has a front-side 102 f and a back-side 102 b. The first semiconductor substrate 102 comprises a first doped region 104 having a first doping type (e.g., p-type/n-type). A photodetector 106 (e.g., a photodiode) is disposed in the first semiconductor substrate 102. The photodetector 106 is configured to absorb incident radiation (e.g., photons) and generate electrical signals corresponding to the incident radiation. A first isolation structure 108 is disposed in the first semiconductor substrate 102 and laterally surrounds the photodetector 106.

A pickup well contact region 110 is disposed in the first doped region 104. The pickup well contact region 110 is a region of the first semiconductor substrate 102 having the first doping type. A floating diffusion node 112 is disposed in the first semiconductor substrate 102 and laterally spaced from the pickup well contact region 110. The floating diffusion node 112 is a region of the first semiconductor substrate 102 having a second doping type (e.g., n-type/p-type) opposite the first doping type.

A transfer gate 114 is disposed in/over the first semiconductor substrate 102 and between opposite sides of the photodetector 106. The transfer gate 114 comprises a transfer gate electrode 116 and a transfer gate dielectric 118. The transfer gate 114 is configured to selectively form a conductive channel between the photodetector 106 and the floating diffusion node 112, such that charge accumulated (e.g., via absorbing incident radiation) in the photodetector 106 may be transferred to the floating diffusion node 112.

A first interlayer dielectric (ILD) structure 120 is disposed over the first semiconductor substrate 102 and the transfer gate 114. In some embodiments, the front-side 102 f of the first semiconductor substrate 102 is the side of the first semiconductor substrate 102 disposed nearest the first ILD structure 120, and the back-side 102 b of the first semiconductor substrate 102 is the side of the first semiconductor substrate 102 opposite the front-side 102 f. In further embodiments, a bonding structure 122 is disposed over the first ILD structure 120.

A second semiconductor substrate 124 is vertically spaced from the first semiconductor substrate 102 and disposed over the first ILD structure 120. The second semiconductor substrate 124 comprises an active region 126. In some embodiments, the active region 126 comprises the first doping type. In other embodiments, the active region 126 may be undoped. In embodiments in which the active region 126 comprises the first doping type, the active region 126 may be referred to as a second doped region. A second isolation structure 128 is disposed in the second semiconductor substrate 124.

A readout transistor 130 (e.g., reset transistor, source follower transistor, row-select transistor, etc.) is disposed on the second semiconductor substrate 124. In some embodiments, the readout transistor 130 comprises a readout gate electrode 132 and a readout gate dielectric 134 that are disposed over the second semiconductor substrate 124. In some embodiments, the readout gate electrode 132 and the readout gate dielectric 134 are referred to a readout transistor gate. The readout gate dielectric 134 separates the readout gate electrode 132 from the second semiconductor substrate 124. In further embodiments, the readout transistor 130 comprises a first pair of source/drain regions 136 a-b disposed in the second semiconductor substrate 124 and on opposite sides of the readout gate dielectric 134. In yet further embodiments, the readout transistor 130 may be, for example, a metal-oxide semiconductor field-effect transistor (MOSFET), a bipolar junction transistor (BJT), a high-electron-mobility transistor (HEMTs), or the like.

A second ILD structure 138 is disposed over the second semiconductor substrate 124 and the readout gate electrode 132. A plurality of first conductive contacts 140 (e.g., metal contacts) are disposed in the second ILD structure 138 and over the second semiconductor substrate 124. A plurality of first conductive lines 142 (e.g., metal lines) are disposed in the second ILD structure 138 and over the first conductive contacts 140. The first conductive contacts 140 provide electrical connections between the readout transistor 130 and some of the first conductive lines 142, respectively.

A plurality of second conductive contacts 144 are disposed over the first semiconductor substrate 102 and extend vertically through the first ILD structure 120 to the second semiconductor substrate 124. The second conductive contacts 144 are electrically coupled to the pickup well contact region 110, the floating diffusion node 112, and the transfer gate electrode 116, respectively. In some embodiments, at least one of the second conductive contacts 144 at least partially provides a conductive path between the pickup well contact region 110, the floating diffusion node 112, or the transfer gate electrode 116 and the readout transistor 130. For example, one of the second conductive contacts 144 may at least partially define a conductive path between the floating diffusion node 112 and a first source/drain region 136 a.

In some embodiments, the second conductive contacts 144 extend vertically through the second semiconductor substrate 124 and into the second ILD structure 138. The second conductive contacts 144 may extend vertically through the second isolation structure 128 and into the second ILD structure 138. In further embodiments, each of the second conductive contacts 144 are electrically coupled to one or more of the first conductive lines 142. In yet further embodiments, the second conductive contacts 144, the first conductive contacts 140, and the first conductive lines 142 may at least partially define a first interconnect structure.

Because the second semiconductor substrate 124 is vertically spaced from the first semiconductor substrate 102, and because the first isolation structure 108 is disposed in the first semiconductor substrate 102 and the readout transistor 130 is disposed on the second semiconductor substrate 124, the first isolation structure 108 may not constrain a size of the readout transistor 130 (e.g., a size of the readout gate electrode 132, the readout gate dielectric 134, and/or the first pair of source/drain regions 136 a-b). Thus, the size of the readout transistor 130 may be larger than if both the readout transistor 130 and the first isolation structure 108 were disposed on a same semiconductor substrate (e.g., the first semiconductor substrate 102). Accordingly, the low-noise image sensor 100 may have improved noise performance.

In addition, because the photodetector 106, the transfer gate 114, and the floating diffusion node 112 are disposed in/over the first semiconductor substrate 102 and the readout transistor 130 is disposed on the second semiconductor substrate 124, the readout transistor 130 may be disposed closer to the floating diffusion node 112 than if both the readout transistor 130 and the floating diffusion node 112 were disposed on a same semiconductor substrate (e.g., the first semiconductor substrate 102). Thus, a total conductive area of the first interconnect structure (e.g., the second conductive contacts 144, the first conductive contacts 140, and the first conductive lines 142) may be less than if both the readout transistor 130 and the floating diffusion node 112 were disposed on the same semiconductor substrate. Accordingly, the low-noise image sensor 100 may have improved noise performance.

FIG. 2 illustrates a layout view of some other embodiments of the low-noise image sensor 100 of FIG. 1. FIG. 2 illustrates the low-noise image sensor 100 without the second ILD structure 138 and the first conductive lines 142. Further, for clarity in FIG. 2, features disposed beneath the second semiconductor substrate 124 (e.g., transfer gate 114, photodetector 106, first isolation structure 108, floating diffusion node 112) are illustrated in phantom by various dashed lines. In addition, for clarity in FIG. 2, the first conductive contacts 140 and the second conductive contacts 144 are illustrated by an “X” disposed in a box. Moreover, for clarity in FIG. 2, the second conductive contacts 144 are illustrated by a larger “X” and corresponding larger box than the first conductive contacts 140.

As shown in FIG. 2, the low-noise image sensor 100 comprises a plurality of photodetectors 106 a-h disposed in the first semiconductor substrate 102. The plurality of photodetectors 106 a-h may comprise a first plurality of the photodetectors 106 a-d, a second plurality of the photodetectors 106 b,c,e,f, and a third plurality of the photodetectors 106 c,f,g,h. For example, the first plurality of the photodetectors 106 a-d comprises a first photodetector 106 a, a second photodetector 106 b, a third photodetector 106 c, and a fourth photodetector 106 d. The second plurality of the photodetectors 106 b,c,e,f may comprise the second photodetector 106 b, the third photodetector 106 c, a fifth photodetector 106 e, and a sixth photodetector 106 f. The third plurality of the photodetectors 106 c,f,g,h may comprise the third photodetector 106 c, the sixth photodetector 106 f, a seventh photodetector 106 g, and an eighth photodetector 106 h.

In some embodiments, the photodetectors of each of the plurality of the photodetectors are disposed in an array having a plurality of rows and columns (e.g., a 2×2 array). For example, the first photodetector 106 a, the second photodetector 106 b, the third photodetector 106 c, and the fourth photodetector 106 d are disposed in a first array 202 a. The second photodetector 106 b, the third photodetector 106 c, the fifth photodetector 106 e, and the sixth photodetector 106 f may be disposed in a second array 202 b.

In some embodiments, the first plurality of the photodetectors 106 a-d, the second plurality of the photodetectors 106 b,c,e,f, and/or the third plurality of the photodetectors 106 c,f,g,h may share one or more of the plurality of photodetectors 106 a-h. For example, the first plurality of the photodetectors 106 a-d, the second plurality of the photodetectors 106 b,c,e,f, and the third plurality of the photodetectors 106 c,f,g,h each comprise the third photodetector 106 c. In other embodiments, the first plurality of the photodetectors 106 a-d, the second plurality of the photodetectors 106 b,c,e,f, and/or the third plurality of the photodetectors 106 c,f,g,h may each have discrete photodetectors.

A plurality of pickup well contact regions 110 a-d are disposed in the first semiconductor substrate 102. The pickup well contact regions 110 a-d correspond to the first plurality of the photodetectors 106 a-d, respectively. For example, a first pickup well contact region 110 a corresponds to the first photodetector 106 a, a second pickup well contact region 110 b corresponds to the second photodetector 106 b, a third pickup well contact region 110 c corresponds to the third photodetector 106 c, and a fourth pickup well contact region 110 d corresponds to the fourth photodetector 106 d.

A plurality of floating diffusion nodes 112 a-d are disposed in the first semiconductor substrate 102. The floating diffusion nodes 112 a-d correspond to the first plurality of the photodetectors 106 a-d, respectively. For example, a first floating diffusion node 112 a corresponds to the first photodetector 106 a, a second floating diffusion node 112 b corresponds to the second photodetector 106 b, a third floating diffusion node 112 c corresponds to the third photodetector 106 c, and a fourth floating diffusion node 112 d corresponds to the fourth photodetector 106 d.

A plurality of transfer gates 114 a-d are disposed in/over the first semiconductor substrate 102. The transfer gates 114 a-d correspond to the first plurality of the photodetectors 106 a-d, respectively. For example, a first transfer gate 114 a corresponds to the first photodetector 106 a, a second transfer gate 114 b corresponds to the second photodetector 106 b, a third transfer gate 114 c corresponds to the third photodetector 106 c, and a fourth transfer gate 114 d corresponds to the fourth photodetector 106 d. It will be appreciated that each of the transfer gates 114 a-d comprise a transfer gate electrode 116 disposed on a transfer gate dielectric 118.

Each of the second conductive contacts 144 are electrically coupled to one of the pickup well contact regions 110 a-d, one of the floating diffusion nodes 112 a-d, or one of the transfer gates 114 a-d. For example, a first one of the second conductive contacts 144 (hereinafter “first conductive contact 144 a”) is electrically coupled to the first floating diffusion node 112 a, a second one of the second conductive contacts 144 (hereinafter “second conductive contact 144 b”) is electrically coupled to the second floating diffusion node 112 b, a third one of the second conductive contacts 144 (hereinafter “third conductive contact 144 c”) is electrically coupled to the third floating diffusion node 112 c, and a fourth one of the second conductive contacts 144 (hereinafter “fourth conductive contact 144 d”) is electrically coupled to the fourth floating diffusion node 112 d. In some embodiments, each of the second conductive contacts 144 that are electrically coupled to one of the pickup well contact regions 110 a-d are configured to provide an electrical connection between the pickup well contact regions 110 a-d and ground (e.g., about 0 Volts (V)).

A plurality of readout transistors 130 a-c are disposed on the second semiconductor substrate 124. For example, a first readout transistor 130 a, a second readout transistor 130 b, and a third readout transistor 130 c are disposed on the second semiconductor substrate 124. A plurality of readout gate electrodes 132 a-c are disposed over the second semiconductor substrate 124. The readout transistors 130 a-c comprise the readout gate electrodes 132 a-c, respectively. A plurality of readout gate dielectrics 134 a-c (not shown in FIG. 2) separate the readout gate electrodes 132 a-c from the second semiconductor substrate 124. For example, the first readout transistor 130 a comprises a first readout gate electrode 132 a and a first readout gate dielectric 134 a, the second readout transistor 130 b comprises a second readout gate electrode 132 b and a second readout gate dielectric 134 b, the third readout transistor 130 c comprises a third readout gate electrode 132 c and a third readout gate dielectric 134 c.

A plurality of source/drain regions 136 are disposed in the second semiconductor substrate 124. The source/drain regions 136 are regions of the second semiconductor substrate 124 having the second doping type. Each of the readout transistors 130 a-c comprise a pair of the source/drain regions 136. For example, the first readout transistor 130 a comprises the first pair of source/drain regions 136 a-b disposed on opposite sides of the first readout gate electrode 132 a, the second readout transistor 130 b comprises a second pair of source/drain regions 136 c-d disposed on opposite sides of the second readout gate electrode 132 b, and the third readout transistor 130 c comprises a third pair of source/drain regions 136 d-e disposed on opposite sides of the third readout gate electrode 132 c. The first pair of source/drain regions 136 a-b comprises the first source/drain region 136 a and a second source/drain region 136 b.

In some embodiments, the second pair of source/drain regions 136 c-d and the third pair of source/drain regions 136 d-e share a source/drain region. For example, the second pair of source/drain regions 136 c-d comprises a third source/drain region 136 c and a fourth source/drain region 136 d, and the third pair of source/drain regions 136 d-e comprises the fourth source/drain region 136 d and a fifth source/drain region 136 e. In other embodiments, the second pair of source/drain regions 136 c-d and the third pair of source/drain regions 136 d-e may each have their own discrete source/drain regions.

The first readout transistor 130 a is at least partially disposed between the first plurality of the photodetectors 106 a-d. In some embodiments, the first readout transistor 130 a is a reset transistor. In such embodiments, the first readout transistor 130 a is configured to provide a reset voltage (e.g., about 5 V) to the first floating diffusion node 112 a, the second floating diffusion node 112 b, the third floating diffusion node 112 c, and/or the fourth floating diffusion node 112 d between exposure periods of incident radiation.

In some embodiments, the first source/drain region 136 a and/or the second source/drain region 136 b are at least partially disposed directly over the first isolation structure 108. In further embodiments, the first source/drain region 136 a and/or the second source/drain region 136 b are entirely disposed directly over the first isolation structure 108. In some embodiments, the first readout gate electrode 132 a (and/or the first readout gate dielectric 1346 a) is at least partially disposed directly over the first isolation structure 108. In further embodiments, the first readout gate electrode 132 a (and/or the first readout gate dielectric 134 a) is disposed directly over both the first isolation structure 108 and the first doped region 104. In yet further embodiments, the first readout gate electrode 132 a (and/or the first readout gate dielectric 134 a) is disposed directly over a first portion of the first doped region 104, which laterally surrounds the first photodetector 106 a; a second portion of the first doped region 104, which laterally surrounds the second photodetector 106 b; a third portion of the first doped region 104, which laterally surrounds the third photodetector 106 c; and a fourth portion of the first doped region 104, which laterally surrounds the fourth photodetector 106 d.

A first one of the first conductive contacts 140 (hereinafter “fifth conductive contact 140 a”) is electrically coupled to the first source/drain region 136 a. A second one of the first conductive contacts 140 (hereinafter “sixth conductive contact 140 b”) is electrically coupled to the first readout gate electrode 132 a. A third one of the first conductive contacts 140 (hereinafter “seventh conductive contact 140 c”) is electrically coupled to the second source/drain region 136 b. In some embodiments, the fifth conductive contact 140 a, the sixth conductive contact 140 b, and/or the seventh conductive contact 140 c are disposed directly over the first isolation structure 108.

A first portion of the active region 126 is disposed beneath the first readout gate electrode 132 a and extends between the first source/drain region 136 a and the second source/drain region 136 b. The first readout transistor 130 a is configured to selectively form a conductive channel in the first portion of the active region 126 that extends between the first source/drain region 136 a and the second source/drain region 136 b. In some embodiments, the first portion of the active region 126 may be referred to as a first well region.

In some embodiments, a first well extension region 204 extends laterally from the first well region in a direction perpendicular to a direction in which the first pair of source/drain regions 136 a-b are spaced apart. The first well extension region 204 is a portion of the active region 126 and is electrically coupled to the first well region. In some embodiments, the first well extension region 204 is at least partially disposed directly over the first isolation structure 108. In further embodiments, the first well extension region 204 is entirely disposed directly over the first isolation structure 108.

A fourth one of the first conductive contacts 140 (hereinafter “eighth conductive contact 140 d”) is electrically coupled to the first well extension region 204. In some embodiments, the eighth conductive contact 140 d is disposed directly over the first isolation structure 108. In further embodiments, the eighth conductive contact 140 d is configured to provide an electrical connection between the first well extension region 204 and ground.

The second readout transistor 130 b is at least partially disposed between the second plurality of the photodetectors 106 b,c,e,f. In some embodiments, the second readout transistor 130 b is a source follower transistor. In such embodiments, the second readout transistor 130 b is configured to selectively output voltages based on charges that are transferred to the second readout transistor 130 b from the first photodetector 106 a, the second photodetector 106 b, the third photodetector 106 c, and/or the fourth photodetector 106 d.

In some embodiments, the third source/drain region 136 c and/or the fourth source/drain region 136 d are at least partially disposed directly over the first isolation structure 108. In further embodiments, the third source/drain region 136 c and/or the fourth source/drain region 136 d are entirely disposed directly over the first isolation structure 108. In some embodiments, the second readout gate electrode 132 b (and/or the second readout gate dielectric 134 b) is at least partially disposed directly over the first isolation structure 108. In further embodiments, the second readout gate electrode 132 b (and/or the second readout gate dielectric 134 b) is disposed directly over the first isolation structure 108, the first doped region 104, and the second plurality of the photodetectors 106 b,c,e,f. In further embodiments, the second readout gate electrode 132 b (and/or the second readout gate dielectric 134 a) is disposed directly over the second portion of the first doped region 104; the third portion of the first doped region 104; a fifth portion of the first doped region 104, which laterally surrounds the fifth photodetector 106 e; and a sixth portion of the first doped region 104, which laterally surrounds the sixth photodetector 106 f. In yet further embodiments, the second readout gate electrode 132 b (and/or the second readout gate dielectric 134 b) is disposed directly over a portion of the second photodetector 106 b, a portion of the third photodetector 106 c, a portion of the fifth photodetector 106 e, and a portion of the sixth photodetector 106 f.

A fifth one of the first conductive contacts 140 (hereinafter “ninth conductive contact 140 e”) is electrically coupled to the third source/drain region 136 c. A sixth one of the first conductive contacts 140 (hereinafter “tenth conductive contact 140 f”) is electrically coupled to the second readout gate electrode 132 b. In some embodiments, the ninth conductive contact 140 e and/or the tenth conductive contact 140 f are disposed directly over the first isolation structure 108.

A second portion of the active region 126 is disposed beneath the second readout gate electrode 132 b and extends between the third source/drain region 136 c and the fourth source/drain region 136 d. The second readout transistor 130 b is configured to selectively form a conductive channel in the second portion of the active region 126. In some embodiments, the second portion of the active region 126 may be referred to as a second well region.

In some embodiments, a second well extension region 206 extends laterally from the second well region in a direction perpendicular to a direction in which the second pair of source/drain regions 136 c-d are spaced apart. The second well extension region 206 is a portion of the active region 126 and is electrically coupled to the second well region. In some embodiments, the second well extension region 206 is at least partially disposed directly over the first isolation structure 108. In further embodiments, the second well extension region 206 is entirely disposed directly over the first isolation structure 108.

A seventh one of the first conductive contacts 140 (hereinafter “eleventh conductive contact 140 g”) is electrically coupled to the second well extension region 206. In some embodiments, the eleventh conductive contact 140 g is disposed directly over the first isolation structure 108. In further embodiments, the eleventh conductive contact 140 g is configured to provide an electrical connection between the second well extension region 206 and ground.

The third readout transistor 130 c is at least partially disposed between the third plurality of the photodetectors 106 c,f,g,h. In some embodiments, the third readout transistor 130 c is a row select transistor. In such embodiments, the third readout transistor 130 c is configured to output a voltage to the second readout transistor 130 b, such that the first photodetector 106 a, the second photodetector 106 b, the third photodetector 106 c, and/or the fourth photodetector 106 d may be read.

In some embodiments, the fifth source/drain region 136 e is at least partially disposed directly over the first isolation structure 108. In further embodiments, the fifth source/drain region 136 e is entirely disposed directly over the first isolation structure 108. In some embodiments, the third readout gate electrode 132 c (and/or the third readout gate dielectric 134 c) is at least partially disposed directly over the first isolation structure 108. In further embodiments, the third readout gate electrode 132 c (and/or the third readout gate dielectric 134 c) is disposed directly over the first isolation structure 108 and the first doped region 104. In yet further embodiments, the third readout gate electrode 132 c (and/or the third readout gate dielectric 134 c) is disposed directly over the third portion of the first doped region 104; the sixth portion of the first doped region 104; a seventh portion of the first doped region 104, which laterally surrounds the seventh photodetector 10 and an eighth portion of the first doped region 104, which laterally surrounds the eighth photodetector 106 h.

An eighth one of the first conductive contacts 140 (hereinafter “twelfth conductive contact 140 h”) is electrically coupled to the fifth source/drain region 136 e. A ninth one of the first conductive contacts 140 (hereinafter “thirteenth conductive contact 140 i”) is electrically coupled to the third readout gate electrode 132 c. In some embodiments, the twelfth conductive contact 140 h and/or the thirteenth conductive contact 140 i are disposed directly over the first isolation structure 108.

A third portion of the active region 126 is disposed beneath the third readout gate electrode 132 c and extends between the fourth source/drain region 136 d and the fifth source/drain region 136 e. The third readout transistor 130 c is configured to selectively form a conductive channel in the third portion of the active region 126. In some embodiments, the third portion of the active region 126 may be referred to as a third well region.

In some embodiments, a third well extension region 208 and a fourth well extension region 210 extend laterally from the third well region in opposite directions that are both perpendicular to a direction in which the third pair of source/drain regions 136 d-e are spaced apart. The third well extension region 208 and the fourth well extension region 210 are portions of the active region 126 and are electrically coupled to the third well region. In some embodiments, the third well extension region 208 and/or the fourth well extension region 210 are at least partially disposed directly over the first isolation structure 108. In further embodiments, the third well extension region 208 and/or the fourth well extension region 210 are entirely disposed directly over the first isolation structure 108. It will be appreciated that, in some embodiments, only one well extension region may extend laterally from the third well region.

A tenth one of the first conductive contacts 140 (hereinafter “fourteenth conductive contact 140 j”) is electrically coupled to the third well extension region 208. An eleventh one of the first conductive contacts 140 (hereinafter “fifteenth conductive contact 140 k”) is electrically coupled to the fourth well extension region 210. In some embodiments, the fourteenth conductive contact 140 j and/or the fifteenth conductive contact 140 k are disposed directly over the first isolation structure 108. In further embodiments, the fourteenth conductive contact 140 j is configured to provide an electrical connection between the third well extension region 208 and ground, and the fifteenth conductive contact 140 k is configured to provide an electrical connection between the fourth well extension region 210 and ground.

FIG. 3 illustrates a layout view of some other embodiments of the first array 202 a of FIG. 2.

As shown in FIG. 3, in some embodiments, the first well extension region 204 is not disposed in the second semiconductor substrate 124. In such embodiments, the eighth conductive contact 140 d may not be disposed over the second semiconductor substrate 124. In further such embodiments, the conducive channels formed by the plurality of readout transistors 130 a-c may extend fully from an upper surface of the second semiconductor substrate 124 to a bottom surface of the second semiconductor substrate 124 (e.g., fully-depleted). In yet further such embodiments, the active region 126 may be undoped or lightly-doped (e.g., having a doping concentration of first doping type dopants that is less than a doping concertation of the first doping type dopants of the first doped region 104).

A floating diffusion nodes contacts (FDNC) region 302 is partially defined by outer sidewalls of the first conductive contact 144 a, the second conductive contact 144 b, the third conductive contact 144 c, and the fourth conductive contact 144 d (hereinafter collectively referred to as “FDN contacts 144 a-d”). For example, a first side of the FDNC region 302 may be defined by a substantially straight line extending from an outer sidewall of the first conductive contact 144 a to an outer sidewall of the second conductive contact 144 b, and a second side of the FDNC region 302 opposite the first side may be defined by a substantially straight line extending from an outer sidewall of the third conductive contact 144 c to an outer sidewall of the fourth conductive contact 144 d. In some embodiments, each of the FDN contacts 144 a-d are entirely disposed within a perimeter of the FDNC region 302.

The FDNC region 302 has a first width W₁ and a first length L₁. In some embodiments, the first length L₁ is between about 120 nanometers (nm) and about 590 nm. The first width W₁ may be between about 120 nm and about 590 nm. In further embodiments, the first length L₁ and the first width W₁ may be about the same. In other embodiments, the first length L₁ and the first width W₁ may be different. In yet further embodiments, an area of the FDNC region 302 is equal to the first length L₁ multiplied by the first width W₁. The area of the FDNC region 302 may be between about 14,400 square nanometers (nm²) and about 348,100 nm².

In some embodiments, a width of each of the FDN contacts 144 a-d is between about 40 nm and about 120 nm. A length of each of the FDN contacts 144 a-d may be between about 40 nm and about 120 nm. In further embodiments, a distance in which two of the FDN contacts 144 a-d are spaced apart is between about 56 nm and about 496 nm. More specifically, the first conductive contact 144 a may be spaced from the second conductive contact 144 b and/or the fourth conductive contact 144 d by between about 40 nm and about 350 nm; the third conductive contact 144 c may be spaced from the second conductive contact 144 b and/or the fourth conductive contact 144 d by between about 40 nm and about 350 nm; the first conductive contact 144 a may be spaced from the third conductive contact 144 c by between about 56 nm and about 496 nm; and/or the second conductive contact 144 b may be spaced from the fourth conductive contact 144 d by between about 56 nm and about 496 nm.

A selectively-conductive channel region 304 is disposed in the second semiconductor substrate 124. The selectively-conductive channel region 304 is part of the first portion of the active region 126 and extends laterally between the first source/drain region 136 a and the second source/drain region 136 b. In some embodiments, the selectively-conductive channel region 304 is defined by the conductive channel that the first readout transistor 130 a selectively forms between the first source/drain region 136 a and the second source/drain region 136 b. In other embodiments, the selectively-conductive channel region 304 may be defined by extending substantially straight lines from opposite sides of the first source/drain region 136 a to opposite sides of the second source/drain region 136 b, respectively.

The selectively-conductive channel has a second width W₂ and a first length L₂. An area of the selectively-conductive channel region 304 is equal to the second length L₂ multiplied by the second width W₂. In some embodiments, at least half of the area of the selectively-conductive channel region 304 is disposed within the perimeter of the FDNC region 302.

A first one of the first conductive lines 142 (hereinafter “first conductive line 142 a”) is disposed over the second semiconductor substrate 124 and the first readout transistor 130 a. In some embodiments, the first conductive line 142 a directly overlies each of the first plurality of the photodetectors 106 a-d, each of the floating diffusion nodes 112 a-d, the first isolation structure 108, and the first source/drain region 136 a. In further embodiments, the first conductive line 142 a is continuous and extends laterally along only a single lateral plane. In yet further embodiments, the first conductive line 142 a may be the nearest conductive line to the FDN contacts 144 a-d and the fifth conductive contact 140 a (e.g., metal 1). In other embodiments, other conductive lines may be disposed between the FDN contacts 144 a-d and the first conductive line 142 a (e.g., the first conductive line 142 a may be on metal 2, 3, 4, etc.).

In some embodiments, the FDN contacts 144 a-d and the fifth conductive contact 140 a are electrically coupled to the first conductive line 142 a. In other words, the first conductive line 142 a electrically couples each of the FDN contacts 144 a-d and the fifth conductive contact 140 a together. In such embodiments, the FDN contacts 144 a-d extend entirely through the first ILD structure 120, entirely through the second semiconductor substrate 124 (or the second isolation structure 128), and into the second ILD structure 138 to electrically couple the floating diffusion nodes 112 a-d to the first conductive line 142 a. For clarity, some of the conductive contacts (e.g., the FDN contacts 144 a-d and the fifth conductive contact 140 a) are illustrated by a six-sided asterisk disposed in a box to illustrate such conductive contacts are electrically coupled together.

Because at least half of the area of the selectively-conductive channel region 304 is within the perimeter of the FDNC region 302, and because the FDN contacts 144 a-d and the fifth conductive contact 140 a are electrically coupled to the first conductive line 142 a, the total conductive area of the first interconnect structure may be further reduced. Accordingly, the noise performance of the low-noise image sensor 100 may be further improved.

FIG. 4 illustrates a layout view of some other embodiments of the first array 202 a of FIG. 3.

As shown in FIG. 4, both the first well extension region 204 and a fifth well extension region 402 extend laterally from the first well region. The fifth well extension region 402 extends in an opposite direction than the first well extension region 204. The fifth well extension region 402 is a portion of the active region 126 and is electrically coupled to the first well region. In some embodiments, the fifth well extension region 402 is at least partially disposed directly over the first isolation structure 108. In further embodiments, the fifth well extension region 402 is entirely disposed directly over the first isolation structure 108.

A twelfth one of the first conductive contacts (hereinafter “sixteenth conductive contact 140 m”) is electrically coupled to the fifth well extension region 402. In some embodiments, the sixteenth conductive contact 140 m is disposed directly over the first isolation structure 108. In further embodiments, the sixteenth conductive contact 140 m is configured to provide an electrical connection between the fifth well extension region 402 and ground.

FIG. 5 illustrates a layout view of some other embodiments of the first array 202 a of FIG. 3.

As shown in FIG. 5, a third doped region 502 is disposed in the second semiconductor substrate 124. The third doped region 502 is a portion of the second semiconductor substrate 124 having the second doping type. The third doped region 502 directly contacts the first source/drain region 136 a, such that the third doped region 502 is electrically coupled to the first source/drain region 136 a.

In some embodiments, the FDN contacts 144 a-d and the fifth conductive contact 140 a are electrically coupled to the third doped region 502. In other words, the third doped region 502 electrically couples each of the FDN contacts 144 a-d and the fifth conductive contact 140 a together. In such embodiments, the FDN contacts 144 a-d may not extend entirely through the second semiconductor substrate 124. Rather, the FDN contacts 144 a-d may extend through the first ILD structure 120 and to (or partially into) the second semiconductor substrate 124 to electrically couple the floating diffusion nodes 112 a-d to the third doped region 502. Because the FDN contacts 144 a-d and the fifth conductive contact 140 a are electrically coupled to the third doped region 502, the total conductive area of the first interconnect structure may be further reduced. Accordingly, the noise performance of the low-noise image sensor 100 may be further improved.

FIG. 6 illustrates a layout view of some other embodiments of the second array 202 b of FIG. 2.

As shown in FIG. 6, both the second well extension region 206 and a sixth well extension region 602 extend laterally from the second well region. The sixth well extension region 602 extends in an opposite direction than the second well extension region 206. The sixth well extension region 602 is a portion of the active region 126 and is electrically coupled to the second well region. In some embodiments, the sixth well extension region 602 is at least partially disposed directly over the first isolation structure 108. In further embodiments, the sixth well extension region 602 is entirely disposed directly over the first isolation structure 108.

A thirteenth one of the first conductive contacts (hereinafter “seventeenth conductive contact 140 n”) is electrically coupled to the sixth well extension region 602. In some embodiments, the seventeenth conductive contact 140 n is disposed directly over the first isolation structure 108. In further embodiments, the seventeenth conductive contact 140 n is configured to provide an electrical connection between the sixth well extension region 602 and ground.

In some embodiments, a fourteenth one of the first conductive contacts (hereinafter “eighteenth conductive contact 140 o”) is electrically coupled to the fourth source/drain region 136 d. In further embodiments, the eighteenth conductive contact is disposed directly over the first isolation structure 108.

FIG. 7 illustrates a layout view of some other embodiments of the second array 202 b of FIG. 6.

As shown in FIG. 7, in some embodiments, only the second well extension region 206 extends laterally from the second well region. It will be appreciated that, in some embodiments, only the sixth well extension region 602 may extend laterally from the second well region.

FIG. 8 illustrates a cross-sectional view of some embodiments of the low-noise image sensor 100 of FIG. 2 taken along line A-A′.

As shown in FIG. 8, the low-noise image sensor 100 comprises a plurality of sidewall spacers 702 a-d. The sidewall spacers 702 a-d are disposed along sidewalls of the transfer gate electrode 116 and the readout gate electrodes 132 a-c. For example, a first sidewall spacer 702 a is disposed over the first semiconductor substrate 102 and along sidewalls of the transfer gate electrode 116; a second sidewall spacer 702 b is disposed over the second semiconductor substrate 124 and along sidewalls of the first readout gate electrode 132 a and sidewalls of the first readout gate dielectric 134 a; a third sidewall spacer 702 c is disposed over the second semiconductor substrate 124 and along sidewalls of the second readout gate electrode 132 b and sidewalls of the second readout gate dielectric 134 b; and a fourth sidewall spacer 702 d is disposed over the second semiconductor substrate 124 and along sidewalls of the third readout gate electrode 132 c and sidewalls of the third readout gate dielectric 134 c. In some embodiments, the sidewall spacers 702 a-d may comprise, for example, a nitride (e.g., silicon nitride (SiN)), an oxy-nitride (e.g., silicon oxy-nitride (SiO_(X)N_(Y))), or the like.

The second ILD structure 138 comprises a lower ILD structure 704 and an upper ILD structure 706. The lower ILD structure 704 separates the upper ILD structure 706 from the second semiconductor substrate 124. In some embodiments, the lower ILD structure 704 has an upper surface that is substantially co-planar with upper surfaces of the first conductive contacts 140 and upper surfaces of the second conductive contacts 144.

In some embodiments, the first conductive lines 142, a plurality of first conductive vias 708 (e.g., metal vias), and a plurality of first contact pads 710 (e.g., metal contact pads) are disposed in the upper ILD structure 706. It will be appreciated that, in some embodiments, any number of first conductive lines 142 and first conductive vias 708 may be stacked in the upper ILD structure 706. In further embodiments, the upper ILD structure 706 has an upper surface that is substantially co-planar with upper surfaces of the first contact pads 710. The first conductive contacts 140, the second conductive contacts 144, the first conductive lines 142, the first conductive vias 708, and the first contact pads 710 are electrically coupled together in a predefined manner and configured to provide electrical connections between the various devices disposed on/over the first semiconductor substrate 102 and the second semiconductor substrate 124 (e.g., the floating diffusion nodes 112 a-d, the transfer gates 114 a-d, the pickup well contact regions 110 a-d, the readout transistors 130 a-c). In yet further embodiments, the first conductive vias 708 and the first contact pads 710 may at least partially define the first interconnect structure.

An integrated chip (IC) 712 is disposed over the second ILD structure 138, the second semiconductor substrate 124, and the first semiconductor substrate 102. In some embodiments, the IC 712 comprises an application-specific integrated circuit (ASIC). The IC 712 comprises a third semiconductor substrate 714. A plurality of semiconductor devices 716 a-c (e.g., p-channel MOSFETs, n-channel MOSFETs, etc.) are disposed on the third semiconductor substrate 714. In some embodiments, the semiconductor devices 716 a-c are image processing devices configured to process signals output by the readout transistors 130 a-c. In further embodiments, a third isolation structure 718 is disposed in the third semiconductor substrate 714 and between the semiconductor devices 716 a-c.

A third ILD structure 720 is disposed between the third semiconductor substrate 714 and the second ILD structure 138. A plurality of third conductive contacts 722 (e.g., metal contacts), a plurality of second conductive lines 724 (e.g., metal lines), a plurality of second conductive vias 726 (e.g., metal vias), and a plurality of second contact pads 728 (e.g., metal contact pads) are disposed in the third ILD structure 720. In some embodiments, the third ILD structure has a lower surface that is substantially co-planar with lower surfaces of the second contact pads 728. The third conductive contacts 722, the second conductive lines 724, the second conductive vias 726, and the second contact pads 728 are electrically coupled together in a predefined manner and configured to provide electrical connections between the various devices disposed on the third semiconductor substrate 714 (e.g., the semiconductor devices 716 a-c). In further embodiments, the third conductive contacts 722, the second conductive lines 724, the second conductive vias 726, and the second contact pads 728 may at least partially define a second interconnect structure.

The third ILD structure 720 is bonded to the second ILD structure 138. The first contact pads 710 are bonded to the second contact pads 728, respectively, such that the first contact pads 710 are electrically coupled to the second contact pads 728, respectively. Accordingly, the transfer gates 114 a-d, the readout transistors 130 a-c, and the semiconductor devices 716 a-c may be electrically coupled together in a predefined manner via the first and second interconnect structures. In some embodiments, the bonded together first contact pads 710 and second contact pads 728 are referred to as bonded contact pads.

The first transfer gate 114 a is disposed between opposite sides of the first photodetector 106 a. The transfer gate dielectric 118 of the first transfer gate 114 a is disposed between the transfer gate electrode 116 of the first transfer gate 114 a and the first photodetector 106 a. In some embodiments, the first transfer gate 114 a is disposed between the first pickup well contact region 110 a and the first floating diffusion node 112 a. In further embodiments, the first transfer gate 114 a extends vertically through the front-side 102 f of the first semiconductor substrate 102, such that the front-side 102 f of the first semiconductor substrate 102 is disposed between an upper surface and a lower surface of the transfer gate electrode 116 of the first transfer gate 114 a. An upper surface of the transfer gate dielectric 118 of the first transfer gate 114 a may be substantially co-planar with the front-side 102 f of the first semiconductor substrate 102. In further embodiments, the first pickup well contact region 110 a is disposed between opposite sides of the first photodetector 106 a. In yet further embodiments, one of the second conductive contacts 144 is electrically coupled to the first pickup well contact region 110 a, and another one of the second conductive contacts 144 is electrically coupled to the transfer gate electrode 116 of the first transfer gate 114 a.

In some embodiments, the first semiconductor substrate 102, the second semiconductor substrate 124, and the third semiconductor substrate 714 may comprise any type of semiconductor body (e.g., monocrystalline silicon/CMOS bulk, silicon-germanium (SiGe), silicon on insulator (SOI), etc.). In further embodiments, a thickness of the second semiconductor substrate 124 may be less than a thickness of the first semiconductor substrate 102 and/or the third semiconductor substrate 714. In yet further embodiments, the thickness of the second semiconductor substrate 124 may be such that the conducive channels formed by the plurality of readout transistors 130 a-c may extend fully from the upper surface of the second semiconductor substrate 124 to the bottom surface of the second semiconductor substrate 124 (e.g., fully-depleted) or may extend partially between the upper surface of the second semiconductor substrate 124 and the lower surface of the second semiconductor substrate 124 (e.g., partially-depleted).

In some embodiments, each of the plurality of photodetectors 106 a-h may comprise a photodetector collector region (not shown) that has a second doping type (e.g., n-type) different than the first doping type. In further embodiments, the pickup well contact regions 110 a-d may have a higher doping concentration of first doping type dopants than the first doped region 104. The pickup well contact regions 110 a-d are configured to provide regions of low resistance between conductive contacts and the first doped region 104. In yet further embodiments, the first isolation structure 108 may be a back-side deep trench isolation (BDTI) structure that extends fully or partially through the first semiconductor substrate 102.

In some embodiments, the transfer gate electrode 116 and the readout gate electrodes 132 a-c may comprise, for example, doped polysilicon (e.g., n-type/p-type polysilicon), a metal (e.g., tungsten (W), aluminum (Al), titanium (Ti), molybdenum (Mo), nickel silicide (NiSi), or the like), or the like. In further embodiments, the transfer gate dielectric 118 and the readout gate dielectrics 134 a-c may comprise, for example, an oxide (e.g., silicon dioxide (SiO₂)), a high-k dielectric material (e.g., hafnium oxide (HfO₂), zirconium oxide (ZrO₂), or some other dielectric material with a dielectric constant greater than about 3.9), or the like.

In some embodiments, the second isolation structure 128 and the third isolation structure 718 may be, for example, a shallow trench isolation (STI) structure, a deep trench isolation structure (DTI), or the like. In further embodiments, the first ILD structure 120, the second ILD structure 138, and the third ILD structure 720 comprise one or more stacked ILD layers, which may respectively comprise a low-k dielectric (e.g., a dielectric material with a dielectric constant less than about 3.9), an oxide (e.g., SiO₂), or the like. In further embodiments, the first conductive lines 142, the first conductive vias 708, the first contact pads 710, the second conductive lines 724, the second conductive vias 726, and the second contact pads 728, may comprise, for example, copper (Cu), Al, gold (Au), W, or the like. In yet further embodiments, the first conductive contacts 140, the second conductive contacts 144, and the third conductive contacts 722 may comprise, for example, W, Cu, Al, or the like.

FIG. 9 illustrates a cross-sectional view of some other embodiments of the low-noise image sensor 100 of FIG. 1.

As shown in FIG. 9, an anti-reflection layer 802 is disposed beneath the back-side 102 b of the first semiconductor substrate 102. In some embodiments, the anti-reflection layer 802 contacts the photodetector 106, the first isolation structure 108, and the first doped region 104. The anti-reflection layer 802 is configured to reduce the amount of incident radiation reflected by the first semiconductor substrate 102. In some embodiments, the anti-reflection layer 802 comprises, for example, an oxide, a high-k dielectric, a nitride, or the like. In further embodiments, the anti-reflection layer 802 may comprise a first layer comprising an oxide stacked on a second layer comprising a high-k dielectric, or vice versa.

A plurality of light filters 804 (e.g., an infrared light filter, a red color filter, a blue color filter, a green color filter, etc.) are disposed on the anti-reflection layer 802. In some embodiments, the light filters 804 are arranged in an array below the anti-reflection layer 802. In further embodiments, the light filters 804 are disposed beneath the plurality of photodetectors 106 a-h, respectively. The light filters 804 are configured to transmit specific wavelengths of incident radiation, respectively. For example, a first light filter (e.g., the red color filter) may transmit light having wavelengths within a first range, while a second light filter (e.g., the blue color filter) may transmit light having wavelengths within a second range different than the first range. Further, a plurality of micro-lenses 806 are disposed on the light filters 804, respectively. The micro-lenses 806 are configured to focus incident radiation towards the plurality of photodetectors 106 a-h, respectively.

FIG. 10 illustrates a cross-sectional view of some other embodiments of the low-noise image sensor 100 of FIG. 9.

As shown in FIG. 10, the transfer gate 114 does not extend into the first semiconductor substrate 102. Rather, the transfer gate 114 is disposed over the first semiconductor substrate 102. In such embodiments, the transfer gate 114 may be referred to as a planar transfer gate. In further such embodiments, both the transfer gate dielectric 118 and the transfer gate electrode 116 may be disposed over the first semiconductor substrate 102. In yet further such embodiments, a doped channel region 902 comprising the second doping type is disposed in the first semiconductor substrate 102. The doped channel region 902 is disposed directly between the photodetector 106 and the transfer gate 114.

FIG. 11 illustrates a cross-sectional view of some other embodiments of the low-noise image sensor 100 of FIG. 9.

As shown in FIG. 11, an upper surface of the anti-reflection layer 802 is non-planar. In such embodiments, the anti-reflection layer 802 may extend into the first semiconductor substrate 102 from beneath the back-side 102 b of the first semiconductor substrate 102. In some embodiments, the anti-reflection layer 802 comprises a first anti-reflection layer 802 a and a second anti-reflection layer 802 b. In some embodiments, the first anti-reflection layer 802 a may comprise, for example, a high-k dielectric, a nitride, or the like. In further embodiments, the second anti-reflection layer 802 b may comprise, for example, an oxide, such as SiO₂, or the like.

FIG. 12 illustrates a cross-sectional view of some other embodiments of the low-noise image sensor 100 of FIG. 9.

As shown in FIG. 12, the first isolation structure 108 extends only partially through the first semiconductor substrate 102. In such embodiments, the first doped region 104 may be disposed between upper surfaces of the first isolation structure 108 and the front-side 102 f of the first semiconductor substrate 102.

FIG. 13 illustrates a cross-sectional view of some other embodiments of the low-noise image sensor 100 of FIG. 9.

As shown in FIG. 13, the first isolation structure 108 is not disposed in the first semiconductor substrate 102. Rather, only portions of the first semiconductor substrate (e.g., portions of the first doped region 104) may be disposed on opposite sides of the photodetector 106.

FIGS. 14-28 illustrate a series of cross-sectional views of some embodiments for forming the low-noise image sensor 100 of FIG. 9.

As shown in FIG. 14, a first semiconductor substrate 102 is provided and a photodetector 106 is formed in the first semiconductor substrate 102. In some embodiments, before the photodetector 106 is formed, a first doped region 104 having a first doping type (e.g., p-type/n-type) is formed in the first semiconductor substrate 102. In further embodiments, a process for forming the first doped region 104 comprises performing a first implant process (e.g., a blanket ion implantation process) to implant first doping type dopants (e.g., p-type dopants) into the first semiconductor substrate 102. The photodetector 106 is a region of the first semiconductor substrate 102 having a second doping type (e.g., n-type/p-type) opposite the first doping type. In some embodiments, the photodetector 106 may be formed by a selective implant process (e.g., a selective ion implantation process) that utilizes a first masking layer (not shown) on the front-side 102 f of the first semiconductor substrate 102 to selectively implant second doping type dopants (e.g., n-type dopants) into the first semiconductor substrate 102. Subsequently, in some embodiments, the first masking layer is stripped away. In further embodiments, a doped channel region 902 may be formed in the first semiconductor substrate 102. The doped channel region 902 may be formed between a portion of the photodetector 106 and the front-side 102 f of the first semiconductor substrate 102. The doped channel region 902 may be formed by a selective implant process that utilizes a second masking layer (not shown) on the front-side 102 f of the first semiconductor substrate 102 and partially covering the photodetector 106 to selectively implant the second doping type dopants into the first semiconductor substrate 102. Subsequently, in some embodiments, the second masking layer is stripped away.

As shown in FIG. 15, a transfer gate 114 is formed in/over the first semiconductor substrate 102. In some embodiments, a process for forming the transfer gate 114 comprises selectively etching the first semiconductor substrate 102 to form a transfer gate opening that extends into the first semiconductor substrate 102 from the front-side 102 f of the first semiconductor substrate 102. In further embodiments, selectively etching the first semiconductor substrate 102 comprises forming a masking layer (not shown) on the front-side 102 f of the first semiconductor substrate 102, and subsequently exposing the first semiconductor substrate 102 to an etchant (e.g., wet/dry etchant) configured to selectively remove unmasked portions of the first semiconductor substrate 102.

Thereafter, a gate dielectric layer (not shown) is deposited or grown on the front-side 102 f of the first semiconductor substrate 102 and lining the transfer gate opening. In some embodiments, the gate dielectric layer may be deposited or grown by, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), thermal oxidation, sputtering, some other deposition or growth process, or a combination of the foregoing. In further embodiments, a planarization process (e.g., chemical-mechanical polishing (CMP)) may be performed into the gate dielectric layer, thereby forming the transfer gate dielectric 118.

Thereafter, a gate electrode layer may be deposited on the front-side 102 f of the first semiconductor substrate 102 and on the transfer gate dielectric 118. In some embodiments, the gate dielectric layer may be deposited by, for example, CVD, PVD, ALD, sputtering, electrochemical plating, electroless plating, some other deposition process, or a combination of the foregoing. In some embodiments, the transfer gate electrode 116 may be formed by a selective etch process that utilizes a masking layer (not shown) on the gate electrode layer to selectively expose the gate electrode layer to an etchant (e.g., wet/dry etchant) that removes unmasked portions of the gate electrode layer. Subsequently, in some embodiments, the masking layer is stripped away. It will be appreciated that, in some embodiments, the selective etch process may be utilized to form the transfer gate dielectric 118.

As shown in FIG. 16, a first sidewall spacer of a plurality of sidewall spacers 702 is formed over the first semiconductor substrate 102 and along sides of the transfer gate electrode 116. Further, a pickup well contact region 110 and a floating diffusion node 112 are formed in the first semiconductor substrate 102. The pickup well contact region 110 is a region of the first semiconductor substrate 102 having a higher doping concentration of the first doping type dopants than the first doped region 104. The floating diffusion node 112 is a region of the first semiconductor substrate 102 having the second doping type.

In some embodiments, the first sidewall spacer may be formed by depositing a first spacer layer (not shown) over the first semiconductor substrate 102 and covering the transfer gate electrode 116. In further embodiments, the first spacer layer may be deposited by PVD, CVD, ALD, sputtering, or the like. The first spacer layer is subsequently etched to remove the first spacer layer from horizontal surfaces, leaving the first spacer layer along opposing sides of the transfer gate electrode 116, as the first sidewall spacer. In various embodiments, the first spacer layer may comprise, for example, a nitride (e.g., SiN), an oxy-nitride (e.g., SiO_(X)N_(Y)), or the like.

In some embodiments, the pickup well contact region 110 may be formed by a first selective implant process that utilizes a first masking layer (not shown) on the front-side 102 f of the first semiconductor substrate 102 and on the transfer gate 114 to selectively implant the first doping type dopants into the first semiconductor substrate 102. Subsequently, in some embodiments, the first masking layer is stripped away. In further embodiments, the floating diffusion node 112 may be formed by a second selective implant process that utilizes a second masking layer (not shown) on the front-side 102 f of the first semiconductor substrate 102 and on the transfer gate 114 to selectively implant the second doping type dopants into the first semiconductor substrate 102. Subsequently, in some embodiments, the second masking layer is stripped away.

As shown in FIG. 17, a first ILD structure 120 is formed over the first semiconductor substrate 102 and the transfer gate 114. In some embodiments, the first ILD structure 120 may be formed with a substantially planar upper surface. In further embodiments, a process for forming the first ILD structure 120 comprises depositing an ILD layer on the first semiconductor substrate 102 and covering the transfer gate 114. The ILD layer may be deposited by CVD, PVD, sputtering, or some other deposition process. Thereafter, a planarization process (e.g., CMP) may be performed on the ILD layer.

As shown in FIG. 18, a second semiconductor substrate 124 comprising an active region 126 is provided and bonded to the first semiconductor substrate 102. A bonding structure 122 is disposed on the second semiconductor substrate 124. In some embodiments, the bonding structure 122 may comprise, for example, an oxide (e.g., SiO₂), a nitride (e.g., SiN), an oxy-nitride (e.g., SiO_(X)N_(Y)), or the like. In further embodiments, a process for bonding the second semiconductor substrate 124 to the first semiconductor substrate 102 comprises positioning the second semiconductor substrate 124 so that the bonding structure 122 faces the first ILD structure 120. Thereafter, the bonding structure 122 is directly bonded to the first ILD structure 120 (e.g., via a direct bonding process).

As shown in FIG. 19, the second semiconductor substrate 124 is thinned. In some embodiments, the second semiconductor substrate 124 may be thinned so that a thickness of the second semiconductor substrate 124 is less than a thickness of the first semiconductor substrate 102. In further embodiments, the second semiconductor substrate 124 may be thinned to a thickness less than about 100 micrometers (um), less than about 10 um, less than about 1 um, or less than about 100 nm. In yet further embodiments, the second semiconductor substrate 124 may be thinned by, for example, grinding, CMP, or some other thinning process. It will be appreciated that, in embodiments in which the active region is doped (e.g., having the first doping type), the active region 126 may be formed before or after the second semiconductor substrate 124 is bonded to the first semiconductor substrate 102 (e.g., via an ion implantation process).

As shown in FIG. 20, a second isolation structure 128 is formed in the second semiconductor substrate 124. In some embodiments, the second isolation structure 128 may be formed by selectively etching the second semiconductor substrate 124 to form an isolation structure opening in the second semiconductor substrate 124, and subsequently filing the isolation structure opening with a dielectric material. In further embodiments, the second semiconductor substrate 124 is selectively etched by forming a masking layer (not shown) on the second semiconductor substrate 124, and subsequently exposing the second semiconductor substrate 124 to an etchant configured to selectively remove unmasked portions of the second semiconductor substrate 124. In yet further embodiments, the dielectric material may comprise an oxide (e.g., SiO₂), a nitride, a carbide, or the like.

As shown in FIG. 21, a readout gate dielectric 134 and a readout gate electrode 132 are formed over the second semiconductor substrate 124. In some embodiments, a process for forming the readout gate dielectric 134 and the readout gate electrode 132 comprises depositing and/or growing (e.g., by CVD, PVD, ALD, thermal oxidation, sputtering, etc.) a readout gate dielectric layer (not shown) on the second semiconductor substrate 124. Thereafter, a readout gate electrode layer (not shown) may be deposited (e.g., by CVD, PVD, ALD, sputtering, electrochemical plating, electroless plating, etc.) on the readout gate dielectric layer. Subsequently, the readout gate dielectric layer and the readout gate electrode layer are selectively etched by utilizing a masking layer (not shown) on the readout gate electrode layer, thereby forming the readout gate dielectric 134 and the readout gate electrode 132, respectively. Subsequently, in some embodiments, the masking layer is stripped away.

As shown in FIG. 22, a second sidewall spacer of the plurality of sidewall spacers 702 is formed over the second semiconductor substrate 124 and along sides of the readout gate electrode 132 and the readout gate dielectric 134. Further, a first pair of source/drain regions 136 a-b are formed in the second semiconductor substrate 124. The first pair of source/drain regions 136 a-b are portions of the second semiconductor substrate 124 having the first doping type or the second doping type. In some embodiments, the first pair of source/drain regions 136 a-b have an opposite doping type than the active region 126.

In some embodiments, the second sidewall spacer may be formed by depositing a second spacer layer (not shown) over the second semiconductor substrate 124 and covering the readout gate electrode 132 and the readout gate dielectric 134. In further embodiments, the second spacer layer may be deposited by PVD, CVD, ALD, sputtering, or the like. The second spacer layer is subsequently etched to remove the second spacer layer from horizontal surfaces, leaving the second spacer layer along opposing sides of the readout gate electrode 132 and opposing sides of the readout gate dielectric 134, as the second sidewall spacer. In various embodiments, the second spacer layer may comprise, for example, a nitride (e.g., SiN), an oxy-nitride (e.g., SiO_(X)N_(Y)), or the like

In some embodiments, the first pair of source/drain regions 136 a-b may be formed by a selective implant process (e.g., a selective ion implantation process) that utilizes a masking layer (not shown) on the second semiconductor substrate 124 to selectively implant second doping type dopants (or first doping type dopants) into the second semiconductor substrate 124. Subsequently, in some embodiments, the masking layer is stripped away. In further embodiments, the readout gate electrode 132 may be utilized as the masking layer (e.g., self-aligned gate process). In yet further embodiments, after the first pair of source/drain regions 136 a-b are formed, formation of a readout transistor 130 may be complete.

As shown in FIG. 23, a lower ILD structure 704 is formed over the second semiconductor substrate 124 and over the readout transistor 130. In some embodiments, the lower ILD structure 704 may be formed with a substantially planar upper surface. In further embodiments, a process for forming the lower ILD structure 704 comprises depositing an ILD layer on the second semiconductor substrate 124 and covering the readout transistor 130. The ILD layer may be deposited by CVD, PVD, sputtering, or some other deposition process. Thereafter, a planarization process (e.g., CMP) may be performed on the ILD layer.

Also shown in FIG. 23, a plurality of second conductive contacts 144 are formed extending through the lower ILD structure 704, the second semiconductor substrate 124, the bonding structure 122, and the first ILD structure 120. The second conductive contacts 144 are formed extending vertically from the pickup well contact region 110, the transfer gate electrode 116, and the floating diffusion node 112, respectively. In some embodiments, a process for forming the second conductive contacts 144 comprises forming a plurality of first conductive contact openings that correspond to the second conductive contacts 144, respectively. The first conductive contact openings extend through the lower ILD structure 704, the second semiconductor substrate 124, the bonding structure 122, and the first ILD structure 120. The first conductive contact openings may be formed by a selective etch process that utilizes a masking layer (not shown) on the lower ILD structure 704 to selectively expose the lower ILD structure 704, the second semiconductor substrate 124, the bonding structure 122, and the first ILD structure 120 to an etchant that removes unmasked portions of the lower ILD structure 704, the second semiconductor substrate 124, the bonding structure 122, and the first ILD structure 120. Subsequently, in some embodiments, the masking layer is stripped away.

Thereafter, a conductive material (e.g., W) is deposited on the lower ILD structure 704 and filling the first conductive contact openings. Subsequently, a planarization process (e.g., CMP) is performed into the conductive material, thereby forming the second conductive contacts 144. In some embodiments, the conductive material may be deposited by CVD, PVD, ALD, sputtering, electrochemical plating, electroless plating, some other deposition process, or a combination of the foregoing.

As shown in FIG. 24, a plurality of first conductive contacts 140 are formed extending through the lower ILD structure 704. The first conductive contacts 140 are formed extending vertically from the source/drain regions of the pair of source/drain regions 136 a-b and the readout gate electrode 132, respectively. In some embodiments, a process for forming the first conductive contacts 140 comprises forming a plurality of second conductive contact openings extending through the lower ILD structure 704 to the source/drain regions of the first pair of source/drain regions 136 a-b and the readout gate electrode 132, respectively. The second conductive contact openings may be formed by a selective etch process that utilizes a masking layer (not shown) on the lower ILD structure 704 to selectively expose the lower ILD structure 704 to an etchant that removes unmasked portions of the lower ILD structure 704. Subsequently, in some embodiments, the masking layer is stripped away.

Thereafter, a conductive material (e.g., W) is deposited on the lower ILD structure 704 and filling the second conductive contact openings. Subsequently, a planarization process (e.g., CMP) is performed into the conductive material, thereby forming the first conductive contacts 140. In some embodiments, the conductive material may be deposited by CVD, PVD, ALD, sputtering, electrochemical plating, electroless plating, some other deposition process, or a combination of the foregoing.

As shown in FIG. 25, an upper ILD structure 706, a plurality of first conductive lines 142, a plurality of first conductive vias 708, and a plurality of first contact pads 710 are formed over the lower ILD structure 704, the first conductive contacts 140, and the second conductive contacts 144. The upper ILD structure 706 may be formed with a substantially planar upper surface. In some embodiments, a process for forming the upper ILD structure 706 comprises depositing a plurality of ILD layers, which are stacked on one another, over the lower ILD structure 704, the first conductive contacts 140, and the second conductive contacts 144. The ILD layers may be deposited by CVD, PVD, sputtering, some other deposition process, or a combination of the foregoing. In further embodiments, a planarization process (e.g., CMP) may be performed on one or more of the plurality of ILD layers.

In some embodiments, a process for forming the first conductive lines 142, the first conductive vias 708, and the first contact pads 710 comprises forming a first ILD layer over the lower ILD structure 704, the first conductive contacts 140, and the second conductive contacts 144. The first ILD layer is selectively etched to form a first set of conductive line openings (not shown) that correspond to a first set of the first conductive lines 142. A conductive material (e.g., Cu) is deposited on the first ILD layer and filling the first set of conductive line openings. A planarization process (e.g., CMP) is performed into the conductive material, thereby forming the first set of the first conductive lines 142.

Thereafter, a second ILD layer is formed over the first set of conductive lines and the first ILD layer. The second ILD layer is selectively etched to form a first set of conductive via openings (not shown) that correspond to a first set of the first conductive vias 708. A conductive material (e.g., Cu) is deposited on the second ILD layer and filling the first set of conductive via openings. A planarization process (e.g., CMP) is performed into the conductive material, thereby forming the first set of the first conductive vias 708. This process (e.g., alternating formation of conductive lines and vias) is repeated until the first conductive lines 142 and the first conductive vias 708 are formed.

Thereafter, a third ILD layer is formed over the first conductive lines 142, the first ILD layer, the first conductive vias 708, and the second ILD layer. The third ILD layer is selectively etched to form a plurality of contact pad openings (not shown) that correspond to the first contact pads 710, respectively. A conductive material (e.g., Cu, Au, etc.) is deposited on the third ILD layer and filling the contact pad openings. A planarization process (e.g., CMP) is performed into the conductive material, thereby forming the first contact pads 710. In yet further embodiments, after the upper ILD structure 706 is formed, formation of a second ILD structure 138 may be complete.

As shown in FIG. 26, an integrated chip (IC) 712 is bonded to the bonded together first and second semiconductor substrates. In some embodiments, the IC 712 comprises a third semiconductor substrate 714, a plurality of semiconductor devices 716 a-b, a third isolation structure 718, a third ILD structure 720, a plurality of third conductive contacts 722, a plurality of second conductive lines 724, a plurality of second conductive vias 726, and a plurality of second contact pads 728. In further embodiments, a process for bonding the IC 712 to the bonded together first and second semiconductor substrates comprises positioning the IC 712 so that the second contact pads 728 are substantially aligned with and face the first contact pads 710, respectively. Thereafter, the first contact pads 710 are directly bonded to the second contact pads 728, respectively (e.g., via a hybrid bonding process, a direct bonding process, etc.). As shown in FIG. 27, a first isolation structure 108 is formed in the first semiconductor substrate 102. Further, in some embodiments, the first semiconductor substrate 102 may be thinned (e.g., via grinding, CMP, or the like). In some embodiments, the first semiconductor substrate 102 may be thinned before the first isolation structure 108 is formed in the first semiconductor substrate 102.

In some embodiments, a process for forming the first isolation structure 108 comprises selectively etching the first semiconductor substrate 102 to form an isolation structure opening in the first semiconductor substrate 102 that extends into the first semiconductor substrate 102 from the back-side 102 b of the first semiconductor substrate 102, and subsequently filling the isolation structure opening (e.g., by CVD, PVD, ALD, thermal oxidation, sputtering, etc.) with a dielectric material. In further embodiments, the first semiconductor substrate 102 is selectively etched by forming a masking layer (not shown) on the back-side 102 b of the first semiconductor substrate 102, and subsequently exposing the first semiconductor substrate 102 to an etchant configured to selectively remove unmasked portions of the first semiconductor substrate 102. In further embodiments, the dielectric material may comprise an oxide (e.g., SiO2), a nitride, a carbide, or the like. In yet further embodiments, a planarization process (e.g., CMP) may be performed into the dielectric material and the first semiconductor substrate 102 to form a substantially planar surface.

As shown in FIG. 28, an anti-reflection layer 802 is formed on the back-side 102 b of the first semiconductor substrate 102. In some embodiments, the anti-reflection layer 802 is formed on the first doped region 104, the photodetector 106, and the first isolation structure 108. In some embodiments, the anti-reflection layer 802 may be formed by CVD, PVD, ALD, sputtering, or the like. Subsequently, in some embodiments, a planarization process (e.g., CMP) may be performed on the anti-reflection layer 802 to planarize an upper surface of the anti-reflection layer 802.

Also shown in FIG. 28, a plurality of light filters 804 (e.g., an infrared light filter, a red color filter, a blue color filter, a green color filter, etc.) are formed on the anti-reflection layer 802. In some embodiments, a center point of one of the light filters 804 is substantially aligned in a vertical direction with a center point of the photodetector 106. In further embodiments, the light filters 804 may be formed by forming various light filter layers over the anti-reflection layer 802 and selectively etching the various light filter layers in a predefined pattern. The light filter layers are formed of a material that allows for the transmission of radiation (e.g., light) having a specific wavelength range, while blocking light of wavelengths outside of the specified range. Subsequently, in some embodiments, a planarization process (e.g., CMP) may be performed on the light filter layers to planarize upper surfaces of the light filter layers.

Also shown in FIG. 28, a plurality of micro-lenses 806 are formed over the light filters 804, respectively. In some embodiments, center points of the micro-lenses 806 are substantially aligned in a vertical direction with center points of the light filters 804, respectively. In further embodiments, the micro-lenses 806 may be formed by depositing a micro-lens material on the light filters 804 (e.g., by a spin-on process, or some other deposition process). A micro-lens template (not shown) having a curved upper surface is patterned above the micro-lens material. In some embodiments, the micro-lens template may comprise a photoresist material exposed using a distributing exposing light dose (e.g., for a negative photoresist more light is exposed at a bottom of the curvature and less light is exposed at a top of the curvature), developed, and baked to form a rounding shape. The micro-lenses 806 are then formed by selectively etching the micro-lens material according to the micro-lens template. In further embodiments, after the micro-lenses 806 are formed, formation of the low-noise image sensor 100 is complete.

FIG. 29 illustrates a flowchart 2900 of some embodiments of a method for forming a low-noise image sensor having stacked semiconductor substrates. While the flowchart 2900 of FIG. 29 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events is not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. Further, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein, and one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

At act 2902, a photodetector is formed in a first semiconductor substrate. FIG. 14 illustrates a cross-sectional view of some embodiments corresponding to act 2902.

At act 2904, a transfer gate is formed on/over the first semiconductor substrate. FIG. 15 illustrates a cross-sectional view of some embodiments corresponding to act 2904.

At act 2906, a floating diffusion node and a pickup well contact region are formed in the first semiconductor substrate. FIG. 16 illustrates a cross-sectional view of some embodiments corresponding to act 2906.

At act 2908, a first interlayer dielectric (ILD) structure is formed over the first semiconductor substrate and the transfer gate. FIG. 17 illustrates a cross-sectional view of some embodiments corresponding to act 2908.

At act 2910, a second semiconductor substrate is bonded to the first semiconductor substrate. FIG. 18 illustrates a cross-sectional view of some embodiments corresponding to act 2910.

At act 2912, a readout transistor is formed on the second semiconductor substrate. FIGS. 18-21 illustrate a series of cross-sectional views of some embodiments corresponding to act 2912.

At act 2914, a lower ILD structure is formed over the second semiconductor substrate and the readout transistor. FIG. 23 illustrates a cross-sectional view of some embodiments corresponding to act 2914.

At act 2916, a plurality of first conductive contacts are formed extending vertically from the floating diffusion node, the transfer gate, and the pickup well contact, respectively, wherein the first conductive contacts extend through the first ILD structure, the second semiconductor substrate, and the lower ILD structure. FIG. 23 illustrates a cross-sectional view of some embodiments corresponding to act 2916.

At act 2918, a plurality of second conductive contacts are formed over the second semiconductor substrate and in the lower ILD structure. FIG. 24 illustrates a cross-sectional view of some embodiments corresponding to act 2918.

At act 2920, an upper ILD structure is formed over the lower ILD structure, the first conductive contacts, and the second conductive contacts, where a plurality of conductive lines, a plurality of conductive vias, and a plurality of contact pads are disposed in the upper ILD structure. FIG. 25 illustrates a cross-sectional view of some embodiments corresponding to act 2920.

At act 2922, an integrated chip (IC) is bonded to the bonded together first and second semiconductor substrates. FIG. 26 illustrates a cross-sectional view of some embodiments corresponding to act 2922.

At act 2924, an isolation structure is formed in the first semiconductor substrate. FIG. 27 illustrates a cross-sectional view of some embodiments corresponding to act 2924.

At act 2926, an anti-reflection layer is formed on the first semiconductor substrate, a plurality of light filters are formed on the anti-reflection layer, and a plurality of micro-lenses are formed on the light filters. FIG. 28 illustrates a cross-sectional view of some embodiments corresponding to act 2926.

In some embodiments, the present application provides an image sensor. The image sensor comprises a first semiconductor substrate comprising a photodetector and a floating diffusion node. A transfer gate is disposed over the first semiconductor substrate, where the transfer gate is at least partially disposed between opposite sides of the photodetector. A second semiconductor substrate is vertically spaced from the first semiconductor substrate, where the second semiconductor substrate comprises a first surface and a second surface opposite the first surface. A readout transistor is disposed on the second semiconductor substrate, where the second surface is disposed between the transfer gate and a gate of the readout transistor. A first conductive contact is electrically coupled to the transfer gate and extending vertically from the transfer gate through both the first surface and the second surface.

In some embodiments, the present application provides an image sensor. The image sensor comprises a plurality of photodetectors disposed in a first semiconductor substrate, where the photodetectors are disposed in an array. A first isolation structure is disposed in the first semiconductor substrate, where the first isolation structure laterally surrounds each of the photodetectors. A second semiconductor substrate is vertically spaced from the first semiconductor substrate and the first isolation structure, where the second semiconductor substrate comprises a first surface and a second surface opposite the first surface. A plurality of floating diffusion nodes are disposed in the first semiconductor substrate, where the floating diffusion nodes are disposed between the second semiconductor substrate and the photodetectors, respectively. A plurality of first conductive contacts are electrically coupled to the floating diffusion nodes, respectively, where the first conductive contacts extend vertically between the second semiconductor substrate and the floating diffusion nodes, respectively. A first readout transistor is disposed on the second semiconductor substrate and at least partially between the first conductive contacts, where the second surface is disposed between the first semiconductor substrate and a first gate of the first readout transistor.

In some embodiments, the present application provides a method for forming an image sensor. The method comprises forming a photodetector in a first semiconductor substrate. A transfer gate is formed over the first semiconductor substrate. A floating diffusion node is formed in the first semiconductor substrate. A first interlayer dielectric (ILD) structure is formed over the first semiconductor substrate and the transfer gate. A bonding layer disposed on a second semiconductor substrate is bonded to the first ILD structure. A readout transistor is formed on the second semiconductor substrate and over the first semiconductor substrate. A second ILD structure is formed over the second semiconductor and the readout transistor. An integrated chip (IC) is bonded to the bonded together first and second semiconductor substrates, where the IC comprises an image processing device, and where both the first ILD structure and the second ILD structure are between the transfer gate and the image processing device.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. An image sensor, comprising: a plurality of photodetectors disposed in a first semiconductor substrate, wherein the photodetectors are disposed in an array; a first isolation structure disposed in the first semiconductor substrate, wherein the first isolation structure laterally surrounds each of the photodetectors; a second semiconductor substrate vertically spaced from the first semiconductor substrate and the first isolation structure, wherein the second semiconductor substrate comprises a first surface and a second surface opposite the first surface; a plurality of floating diffusion nodes disposed in the first semiconductor substrate, wherein the floating diffusion nodes are disposed between the second semiconductor substrate and the photodetectors, respectively; a plurality of first conductive contacts electrically coupled to the floating diffusion nodes, respectively, wherein the first conductive contacts extend vertically between the second semiconductor substrate and the floating diffusion nodes, respectively; a first readout transistor disposed on the second semiconductor substrate and at least partially between the first conductive contacts, wherein the second surface is disposed between the first semiconductor substrate and a first gate of the first readout transistor; and a plurality of second conductive contacts separated from the first semiconductor substrate by the second semiconductor substrate, wherein: the first readout transistor comprises a first pair of source/drain regions disposed in the second semiconductor substrate and on opposite sides of the first gate; the second conductive contacts are electrically coupled to the source/drain regions of the first pair of source/drain regions and to the first gate, respectively; and each of the second conductive contacts overlie the first isolation structure; a plurality of conductive paths directly electrically couple the plurality of floating diffusion nodes to a same source/drain region of the first pair of source/drain regions; and each of the plurality of first conductive contacts at least partially define a corresponding one of the plurality of conductive paths.
 2. The image sensor of claim 1, further comprising: an active region disposed in the second semiconductor substrate and extending continuously between the source/drain regions of the first pair of source/drain regions; and a third conductive contact electrically coupled to the active region, wherein the third conductive contact overlies the first isolation structure and is separated from the first semiconductor substrate by the second semiconductor substrate.
 3. The image sensor of claim 1, wherein the first isolation structure extends completely through the first semiconductor substrate.
 4. The image sensor of claim 1, further comprising: a second isolation structure disposed in the second semiconductor substrate and laterally surrounding the first readout transistor, wherein the first conductive contacts extend vertically through the second isolation structure, such that both the first surface and the second surface are disposed between an upper surface and a lower surface of each of the first conductive contacts.
 5. The image sensor of claim 1, wherein the first readout transistor comprises: a selectively-conductive channel disposed in the second semiconductor substrate and extending between the source/drain regions of the first pair of source/drain regions, wherein at least half of the selectively-conductive channel is disposed between the first conductive contacts.
 6. The image sensor of claim 1, wherein a maximum distance between two conductive contacts of the plurality of first conductive contacts is less than or equal to about 496 nanometers.
 7. The image sensor of claim 1, further comprising: a first set of photodetectors disposed on a first side of the first gate, wherein the first set of photodetectors comprises two photodetectors of the plurality of photodetectors; a second set of photodetectors disposed on a second side of the first gate opposite the first side, wherein the second set of photodetectors comprises two other photodetectors of the plurality of photodetectors; and a second readout transistor disposed on the second semiconductor substrate, wherein a second gate of the second readout transistor is disposed on an opposite side of the first set of photodetectors as the first readout transistor.
 8. The image sensor of claim 7, further comprising: a first active region of the second semiconductor substrate extending continuously between the first pair of source/drain regions; a second pair of source/drain regions disposed in the second semiconductor substrate and on opposite sides of the second gate, wherein a second active region of the second semiconductor substrate extends continuously between the second pair of source/drain regions; a plurality of third conductive contacts separated from the first semiconductor substrate by the second semiconductor substrate, wherein the third conductive contacts are electrically coupled to the source/drain regions of the second pair of source/drain regions and the second gate, respectively, and wherein each of the third conductive contacts overlie the first isolation structure; and a fourth conductive contact electrically coupled to the second active region, wherein the fourth conductive contact is disposed directly over the first isolation structure and separated from the first semiconductor substrate by the second semiconductor substrate.
 9. An image sensor, comprising: a plurality of photodetectors disposed in a first semiconductor substrate, wherein the plurality of photodetectors are disposed in an array; a second semiconductor substrate vertically spaced from the first semiconductor substrate; a plurality of floating diffusion nodes disposed in the first semiconductor substrate, wherein each of the plurality of floating diffusion nodes are disposed between the second semiconductor substrate and a corresponding one of the plurality of photodetectors; a plurality of conductive contacts electrically coupled to the plurality of floating diffusion nodes, respectively, wherein each of the plurality of conductive contacts extend vertically from the first semiconductor substrate to at least the second semiconductor substrate, and wherein outer sidewalls of the plurality of conductive contacts at least partially define a perimeter of a region in which each of the plurality of conductive contacts are disposed within; and a readout transistor disposed on the second semiconductor substrate, wherein: the readout transistor comprises a pair of source/drain regions disposed in the second semiconductor substrate; each of the plurality of conductive contacts are directly electrically coupled to a same one of the source/drain regions of the pair of source/drain regions; the readout transistor comprises a gate disposed between the source/drain regions and over both the first semiconductor substrate and the second semiconductor substrate; and the readout transistor comprises a selectively-conductive channel disposed in the second semiconductor substrate and extending laterally between the source/drain regions, wherein at least half of the selectively-conductive channel is disposed within the perimeter of the region.
 10. An image sensor, comprising: a plurality of photodetectors disposed in a first semiconductor substrate, wherein the plurality of photodetectors are disposed in an array; a second semiconductor substrate vertically spaced from the first semiconductor substrate; a plurality of floating diffusion nodes disposed in the first semiconductor substrate, wherein each of the plurality of floating diffusion nodes are disposed between the second semiconductor substrate and a corresponding one of the plurality of photodetectors; a readout transistor disposed on the second semiconductor substrate, wherein the readout transistor comprises a first source/drain region and a second source/drain region disposed in the second semiconductor substrate, and wherein a plurality of conductive paths directly electrically couple each of the plurality of floating diffusion nodes to the first source/drain region; and a plurality of conductive contacts extending vertically from the first semiconductor substrate to at least the second semiconductor substrate, wherein: each of the plurality of conductive contacts at least partially define a corresponding one of the plurality of conductive paths; outer sidewalls of the plurality of conductive contacts at least partially define a perimeter of a region in which each of the plurality of conductive contacts are disposed; and the readout transistor is at least partially disposed within the perimeter of the region.
 11. The image sensor of claim 10, wherein: the readout transistor comprises a gate electrode disposed laterally between the first source/drain region and the second source/drain region and disposed over both the first semiconductor substrate and the second semiconductor substrate; and the gate electrode is at least partially disposed within the perimeter of the region.
 12. The image sensor of claim 11, wherein: the readout transistor comprises a selectively-conductive channel disposed in the second semiconductor substrate and extending laterally between the first source/drain region and the second source/drain region; and the selectively-conductive channel is at least partially disposed within the perimeter of the region.
 13. The image sensor of claim 12, wherein at least half of the selectively-conductive channel is disposed within the perimeter of the region.
 14. The image sensor of claim 12, wherein the perimeter of the region extends laterally around the selectively-conductive channel in a closed loop path.
 15. The image sensor of claim 10, wherein: the first source/drain region is at least partially disposed within the perimeter of the region.
 16. The image sensor of claim 15, wherein: the second source/drain region is at least partially disposed within the perimeter of the region.
 17. The image sensor of claim 10, wherein the plurality of conductive contacts extend vertically from the plurality of floating diffusion nodes to a doped region of the second semiconductor substrate, wherein each of the plurality of conductive contacts contact the doped region of the second semiconductor substrate at different locations, and wherein the doped region at least partially defines the plurality of conductive paths.
 18. The image sensor of claim 10, further comprising: an interconnect structure comprising a plurality of conductive lines, wherein: the second semiconductor substrate is disposed vertically between the plurality of conductive lines and the first semiconductor substrate; the plurality of conductive contacts extend from the plurality of floating diffusion nodes to a first conductive line of the plurality of conductive lines; and the first conductive line of the plurality of conductive lines at least partially defines the plurality of conductive paths.
 19. The image sensor of claim 18, wherein the interconnect structure further comprises: an upper conductive contact laterally spaced from each of the plurality of conductive contacts, wherein the upper conductive contact extends vertically from the first conductive line of the plurality of conductive lines to the first source/drain region, and wherein the upper conductive contact at least partially defines the plurality of conductive paths.
 20. The image sensor of claim 10, wherein the readout transistor comprises: a selectively-conductive channel disposed in the second semiconductor substrate, wherein the selectively-conductive channel extends laterally between the first source/drain region and the second source/drain region, wherein the first source/drain region is disposed on a first side of the selectively-conductive channel, and wherein the second source/drain region is disposed on a second side of the selectively-conductive channel opposite the first side of the selectively-conductive channel; and a gate electrode disposed over the second semiconductor substrate and laterally between the first source/drain region and the second source/drain region, wherein the gate electrode is configured to control a conductivity of the selectively-conductive channel. 